1. Field of the Invention
The present invention relates to vibration or shock detection for protecting a memory device from disturbance applied to the memory device, and particularly to the function of making a distinction as to the type of disturbance (vibrations and shock) and detecting it.
2. Description of the Related Art
In a magnetic disk device and other memory devices built in a notebook personal computer or a mobile computer, a minimum level to be detected has heretofore been fixed and set in advance to make full use of a shock detecting function of each device. Therefore, the device did not cope with variations in the scale of an actual shock and the cycle of actual vibrations due to a good or bad decision as to the state of its mounting to a system, and shifts or differences in detection sensitivity due to changes in individual characteristics of detection systems every devices and environmental conditions. Further, the device was low in detection accuracy and not capable of avoiding misdetection due to noise.
Incidentally, there is known Japanese Published Unexamined Patent Application No. Hei 11-126412, which corresponds to the Patent Application filed by the same applicant as the present application and relates to a technique capable of resuming a write operation interrupted by the application of a shock after retry waiting for the shortest time corresponding to the amount of the shock.
The scale and components of a shock applied to a memory device vary widely due to the way of placing the memory device in a system, its position and direction, and other factors. There may be cases in which electromagnetic noise, particularly, a pulsated noise signal is misdetected as disturbance. In addition to it, there was a case in which a difference would occur between a detected level and each of actual shock and/or vibrations due to variations in the performance for each device and changes in environmental condition. That is, due consideration has not been given to the fact that misdetection is produced due to vibrations and noise other than a shock to be detected and other disturbance to thereby degrade the performance of the entire device (excessive or over-detection) and the fact that data stored in the memory device will suffer damage due to the deficiency of detection sensitivity (under-detection).
There is provided the function of monitoring the scale and cycle of disturbance to thereby detect harmful disturbance. To this end, information about at least two points are captured from a signal waveform, which is an analog signal waveform corresponding to disturbance and is represented by time-amplitude coordinates, thereby to extract information corresponding to the scale and cycle of the disturbance. Even either analog signal processing or digital signal processing can obtain this function.
A) As to the analog signal processing, for example, an inclination defined by two points on coordinates of time t-amplitude h is monitored as information corresponding to the scale and cycle of disturbance. The above function is produced or exerted owing to the occurrence of the disturbance. Thus, the difference (xcex94h) in amplitude is detected as an analog signal by a hardware circuit from an amplitude value at a time at a first point immediately after its production and an amplitude value after a small time (xcex94t) has elapsed. If xcex94h/xcex94t is greater than or equal to a predetermined value, then a detection signal is outputted as undesired disturbance (shock). If xcex94h/xcex94t is less than the predetermined value, then no detection signal is outputted with the disturbance as allowable vibrations. When it is desired to detect one not high in frequency, of the disturbance, the detection thereof can be implemented even by software as an alternative to hardware.
Exerting (triggering) the function by the disturbance is obtained by an increase in the sensitivity of a shock sensor used as a disturbance sensor. The amplitude of an analog signal corresponding to disturbance at a second point after the elapse of a time xcex94t, is captured based on a trigger subsequent to the removal of cycle-short noise disturbance by a predetermined filter. If xcex94t is settable and only the amplitude at the second point is captured with respect to the constant xcex94t, then the calculation of xcex94h is implemented by a hardware logic circuit. Therefore, a processing speed for its calculation is sufficiently fast for the detection of undesired disturbance. An acceleration sensor comprised of a semiconductor element or a piezoelectric element is used as the shock sensor. Sensors using piezo elements include a voltage type and a capacity (charge) type according to the type of output subsequent to the detection and conversion of disturbance. Both of them change somewhat in circuit configuration of a first amplifier and can be used in applications of the present invention. Incidentally, each waveform illustrated in the present specification is one outputted from the voltage type sensor.
B) As to the digital signal processing on the other hand, for example, the scale and cycle of disturbance are captured as digital data and a conversion table is created in advance based on them. The processing B) is carried out in parallel with the processing A) to thereby allow the storage of disturbance (shock) data while coping with a harmful shock.
Further, a plurality of embodiments each having a disturbance detection circuit or a disturbance detecting function have been disclosed which are configured so as to output slice level values for providing suitable detection sensitivity, based on the data stored in the conversion table or effect correction adjustments thereon and output them. In such embodiments, the circuit comprises hardware elements capable of high-speed operation and detects disturbance with suitable sensitivity corresponding to the disturbance (vibrations or shock). A conversion table is produced according to a statistical procedure and only the table may be mounted in a memory device and detected. That is, the scale and cycle of a shock are grasped or held as digital data and the slice of shock sensitivity is automatically corrected and adjusted by the device per se, whereby misdetection is reduced and the reliability of data protection of the device is enhanced consequently.
Described more specifically, 1) an integrated value and a cycle of an analog waveform of disturbance detected by a shock sensor are sampled at high speed by a peak hold (sample-and-hold) circuit and captured as digital data. 2) A suitable slice value is selected from a conversion table stored in a ROM and another memory element as default values in advance. 3) A command for changing a detection slice voltage is sent out to a detection/determination slice unit capable of changing a detection slice voltage for determining a threshold value for detection. 4) When the digital data corresponding to the disturbance is captured, the range for the scale and cycle of a shock, which makes detection effective, is limited for the sake of the removal of noise (it is waveform-shaped by a low-pass filter). 5) The frequency of occurrence of disturbance, a cumulative value and other information are added to the digital data as history information corresponding to the disturbance. 6) A learning function such as the speeding up of a detecting process or the application of correction to the detecting process is provided to cope with subsequently- generated disturbance. 7) An embodiment of a magnetic disk device will further be explained. When a shock corresponding to undesired disturbance occurs, the amount of overrun of a magnetic head and the rate of generation of an error thereof with respect to the magnitude of the shock are determined according to temperatures, a power source, hours for use, other use environmental conditions, and data read, data write, seek, following and other operation modes or the like. Thus, correction values are individually and specifically calculated according to the type of these parameters and disturbance (shock), and hence the accuracy of disturbance detection and correction-value adjustments can be improved. 8) There is also provided the function of allowing a user to adjust each detected level at random according to a vendor unique command on an interface through a host system within a limited allowable range in which a stable operation can be ensured even if disturbance exists.
According to the technology disclosed in the present invention, since the cycle and amplitude of disturbance are monitored, more specifically, the disturbance is monitored at at least two points on a signal waveform corresponding to the disturbance and the inclination of the rising edge of a disturbance signal is monitored or supervised from their times and amplitude, a shock harmful to a device can be detected and hence distinguished from allowable vibrations.
Further, the device per se can capture the scale and cycle of disturbance (shock/vibrations) as digital data and store them therein. Based on it, the device can output a slice level value for providing suitable detection sensitivity from a conversion table or can provide its output as a corrected/adjusted output. Therefore, the disturbance can be detected correctly with the optimum sensitivity or sensitivity close thereto corresponding to a system equipped with a disturbance detection circuit, its on-board state, environmental conditions and other conditions.